Seal means for isolated ground O2 sensor

ABSTRACT

A sensor (24) having a metal shell (30) joined to a sleeve (96) to locate a heater (92) in a thimble of an electrolyte member (72). A sealed joint is produced between the sleeve (96) and metal shell (30) to define a sealed reference chamber (118). A porous filter (112) in the sleeve (96) prevents water in environmental air from entering the reference chamber (118). Leads (106&#39;) and 106&#34;) which pass through the porous filter (112) are connected to terminal (164 and 164&#39;). Terminals (164 and 164&#39;) located in a terminal member (120) position a heater (92) within chamber (118) and the electrolyte member (72). Leads (106 and 106 n ) which pass through the porous filter are connected to contact rings (142 and 144). Contact rings (142 and 144) are connected to an external and internal coating (80 and 82) on the electrolyte member (72). In response to a signal from a controller (26) electrical current is supplied to the heater (92) to maintain the temperature in chamber (118) above present limits such that changes in the ion conduction through the electrolyte member (72) is accurately measured. The changes result from a difference in the oxygen content of air in the reference chamber (118) as compared with oxygen in an exhaust gas supplied to the external surface (80).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a gas constituent electrochemicalsensor for sensing the concentration of oxygen in an unknown gasrelative to a reference gas. This sensor has a tubular electrolytethimble with an internal and external conductive coating connected to acontrol member. Changes in oxygen concentration in the gas as comparedto the reference concentration creates an operational signal indicativeof air/fuel ratio supplied to an engine. A heater member receiveselectrical current from the control member to maintain the temperatureof the thimble above a minimm operational temperature. As a result, theoperational signal is only dependent on the difference in the oxygenconcentration between the unknown and reference gases.

2. Description of the Prior Art

It is known that a body of solid electrolyte, for example zirconiumdioxide, which has one surface exposed to a reference oxygenconcentration and a second surface exposed to an unknown oxygenconcentration may generate an electrical potential between suchsurfaces. Examples of sensors which use such an electrolyte member maybe found in U.S. Pat. Nos. 3,960,692 and 3,960,693, which issued June 1,1976, U.S. Pat. No. 4,019,974 which issued Apr. 26, 1977 and U.S. Pat.No. Re. 28,792, which reissued Apr. 27, 1976, the disclosures of whichare incorporated herein by reference.

By coating the surface of the zirconium dioxide, or other solidelectrolyte body with a catalytic material, such as platinum, arelatively high output signal can be generated whenever the combustionmixture is at an air/fuel ratio less than the stoichiometric mixtureratio for that fuel and a relatively low signal wherever the mixture isat an air/fuel ratio greater than the stoichiometric mixture ratio forthat fuel. Thus, a generally step function will be generated by thesensor as the air/fuel mixture ratio passes through stoichiometry from arelative low to high value.

Typically, the solid electrolyte, as illustrated in the above referencedpatents, is formed in the shape of a closed ended tube or a thimble. Thethimble is coated on the inside and outside with a porous metallicelectrode material, for example, platinum or palladium. The exterior ofthe closed end tube or thimble is inserted into the exhaust system andexposed to the heated exhaust gas created by the combustion of gaseswithin an internal combustion engine, or is exposed to the incomingair/fuel mixture, while the interior of the close ended tube or thimbleis exposed to atmospheric conditions. Thus, the sensor generates avoltage that is proportional to the difference between the partialpressures of oxygen between the interior and exterior of the electrolytethimble.

The outside surface of the thimble is usually connected to an electricalground through the attachment of the housing of the sensor to theexhaust system. The exhaust system in turn is connected to the chassisof the vehicle to form one of the conductors for a sensor. This typeelectrical ground connection is illustrated by a clip disclosed in U.S.Pat. No. 4,111,778.

Most vehicles use a multiplicity of electrical loads and as a result theelectrical ground conductor for an oxygen sensor may have variouselectrical potential applied thereto and is practically never completelyfree of voltage variations. Unfortunately, the output signal as measuredacross the inner surface terminal of the sensor and outer surfaceterminal grounded to the vehicle may not be the true output from thesensor itself. The electrical loading characteristics and operationalpotential generated by the other electrical components of the vehiclemay therefore change the actual voltage signal as measured in the sensorand could interfere with proper operation of the control system settingof the air/fuel mixture to be supplied to the combustion chamber. Thus,the composition of the exhaust gases being emitted from the engine couldbe adversely affected by this type of sensor construction.

U.S. Pat. No. 4,019,974 attempted to overcome this problem with apositive ground crimped to a terminal connected to the outside surfaceconductor. In this sensor, a resilient conductive mass of graphite ispositioned around the thimble by a mass of insulating powder to providean electrical path between the outside conductive surface and terminalconnector. Unfortunately this structure requires some complicated andexpensive manufacturing in order to maintain the components in theirspacial relationship to assure that an adequate and uninterruptedelectrical flow path is produced between the outside conductive surfaceand the electrical terminal.

SUMMARY OF THE INVENTION

In order to simplify the structure of an oxygen sensor we have devised amethod of manufacture whereby module components are systematicallyjoined together to develop a heated electrochemical sensor having anisolated ground.

In this sensor, a tubular electrochemical thimble member is insertedinto an isolated carrier member in a metal shell. The thimble has itsinternal and external surfaces coated with a conductive material. Asleeve has a closed end with a plurality of openings therein. Lead wiresare brought through a filter located in the sleeve adjacent theopenings. A first terminal is attached to a first wire connected to apower source in a control member and a second terminal is attached to asecond wire to establish an electrical ground in the control member.Third and fourth wires are also carried through passages in acylindrical member. A first contact ring is attached to the third wireand a second contact ring is attached to the fourth wire. The firstcontact ring is placed on an annular projection that extends from thecylindrical member and positioned on a first shoulder. A stepped axialbore extends through the projection into the cylindrical member. Thesecond contact ring is placed in the stepped axial bore and positionedon a second shoulder. The annular projection in addition to electricallyisolating the first and second contact rings forms a guide surface for aspring washer. The cylindrical member has first and second axial grooveslocated on its peripheral surface that extend to first and second radialoffset slots. The radial slots extend at least into the stepped axialbore. The first and second terminal are thereafter pushed into the firstand second radial slots, respectively. A tubular heater member insertedinto the stepped axial bore has a first end with a first contact surfacethat engages the first terminal and a second contact that engages thesecond terminal. A coil spring is placed over the tubular heater and acontact cup located on the end of the coil spring. The contact cup has aseries of prongs or projections that engage the surface of the tubularheater to hold the coil spring and position the tubular heater withinthe thimble of the sensor. A cylindrical contact extension has a firstend with a flange thereon that is positioned on the annular projectionof the terminal member. The heater is aligned with the interior of thetubular electrochemical member and a force is applied to bring a secondend on the contact extension into contact with the internal surface ofthe carrier member while at the same time the contact cup is broughtinto engagement with the internal surface of the electrochemical sensormember. The spring washer and coil spring resiliently urge the terminalmember away from the electrochemical sensor member to provide for anelectrical flow path between the internal and external surfaces of theelectrochemical member and the control member. A series of spot weldsjoin the sleeve to the metal shell. Thereafter, the sleeve is heated tocause a brazing material to flow and form a seal for the joint betweenthe sleeve and metal shell. In an alternate construction, a portion ofthe sleeve may be rolled into a groove in the metal shell to seal thejoint.

An advantage of this oxygen sensor is achieved through the individualassembly of various components that are later joined together in a finalassembly.

A further advantage of this oxygen sensor resides in the terminalstructure which carries leads to both an electrochemical sensor memberand an internal heater associated therewith.

A still further advantage of this oxygen sensor occurs since the sleevewhich carries the terminal structure has a sealed joint with respect toa metal shell and as a result a reference gas must pass through a filterbefore entering into a reference chamber of an electrochemical member.

A still further advantage of this oxygen sensor is provided through theelectrical ground connection for both an electrochemical member and aheater is in a control member to assure that an operational signalgenerated thereon represents a true comparison of an oxygen component ina mixture of exhaust gases with a reference gas.

These advantages and others should be apparent from reading thespecification while viewing the drawings wherein:

FIG. 1 is a schematic illustration of a vehicle engine with anelectrochemical sensor, made according to this invention, located in anexhaust system to provide a fuel management system with an indication ofthe oxygen in exhaust gases; and

FIG. 2 is a sectional view of the electrochemical sensor of FIG. 1; and

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2; and

FIG. 4 is a sectional view taken along line 4--4 of FIG. 2; and

FIG. 5 is a sectional view taken along line 5--5 of FIG. 2; and

FIG. 6 is a perspective view of the terminal member of FIG. 2; and

FIG. 7 is a perspective view of the terminal spade for the heater leadof FIG. 2; and

FIG. 8 is a perspective view of the contact cup of FIG. 2; and

FIG. 9 is an enlarged sectional view of the leads for the terminalspades and contact rings in FIG. 2; and

FIG. 10 is an exploded view of the electrochemical sensor of FIG. 2illustrating a method whereby the individual components are joinedtogether into a final assembly.

FIG. 11 is a partial sectional view of an alternate seal between themetal shell and tubular sleeve for the sensor of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

The internal combustion engine 16 shown in FIG. 1 has an exhaust 18system through which exhaust gases are transmitted from manifold 20through pipe 22 to the surrounding environment. An electrochemicalsensor 24 located in pipe 22 supplies controller 26 with an indicationof the oxygen content of the exhaust gases. The controller 26 providesan electronic fuel metering apparatus 28 with an operational signal tocontrol the air/fuel ratio that is supplied to operate the engine 16.

Changes in the oxygen content in the exhaust gases are experienced bythe electrochemical sensor 24 and transmitted to the controller 26 tomaintain the air/fuel ratio signal to the metering apparatus 28 withinset operational limits to provide for fuel economy in addition tomeeting clean air standards. Both the positive and negative leads forsensor 24 are connected to the controller 26 to prevent any changes inthe electrical ground within the vehicle from affecting the operationalsignal generated from the changes of the oxygen content in the exhaustgases.

The oxygen sensor 24 is shown in more detail in FIGS. 2-9. Sensor 24 hasa metal shell 30 with an axial bore 32 therein. A hexagonal surface 34has a washer 36 that engages boss 38 when threads 40 are screwed intocorresponding threads in the exhaust pipe 22. Metal shell 30 has aperipheral groove 42 adjacent a first end 44 and an internal annularshoulder 46 located between the first end 44 and a second end 48 in theaxial bore 32.

A vented shield 50 has a first end 52 and a second end 53. The secondend 53 has flange 54. The vented shield 50 is inserted in the axial bore32 and flange 54 seated on shoulder 46. A plurality of openings 62, 62'.. . 62^(n) allow exhaust gases to be freely communicated into theinterior 64 of the shield 50.

A support member 55 is placed in the axial bore 32 and engages flange54. Thereafter a sealing and insulating ring 60, e.g. talc, is placed inthe bore 32 adjacent flange 54 on the support member 57. An insulatorspacer 56, a ceramic disc, is placed in the axial bore 32 and engagesring 60. Thereafter an element carrier 66 is located in bore 32. Carrier66 has a cylindrical body with a flange 68 on a first end and aninwardly projecting lip 70 on the other end. The cylindrical body ofcarrier 66 engages the insulator spacer 56 while lip 70 engages the talcring 60.

The sensor element 72 is in the form of a tubular thimble and is made ofan ion conductive solid electrolyte such as zirconium dioxide. Thethimble has a closed end 74 and an opened end 76. An annular externalrib 78 adjacent the opened end 76 engages the lip 70 on the carrier 66.The external surface 80 and internal surface 82 of sensor element 72 arecoated with a porous, electron conductive layer (e.g. platinum) to forma catalyst for gases which will be presented to these surfaces. A porousinsulating protecting coating 81, e.g. spinel, is applied to theexternal surface 80. The internal and external surface coatings 80 and82 are separated at the opened end 76 by an uncoated annular surface 84to assure that separate electrical flow paths are established to permition flow through the thimble. The external conductive coating 80contacts the carrier body 66 and extends the flow path past theinsulator ring or spacer 56 and talc ring 60 while contact cup 86 asbest shown in FIG. 8, is located adjacent the opened end 76 to extendthe interior surface coating 82 while still maintaining the isolationbetween the interior and exterior coatings. When an axial force isapplied to the carrier 66, flange 68 compresses the talc ring 60 to forma seal with the metal shell 30 exterior surface 80 of thimble 72 andcarrier 66.

The contact cup 86 as best shown in FIG. 8 has a series of fingers orprongs 88, 88'. . . 88^(n) engage tubular member 90 on a heater member92 to hold the end 94 of the heater 92 in approximately the radialcenter of the interior of the thimble 72 as shown in FIG. 5.

A sleeve 96 has a closed end 98 and an opened end 100. The sleeve 96 hasa flare 102 on the opened end 100 and a plurality of openings 104, 104'.. . 104^(n) in the closed end 98. A first diameter section 95 of sleeve96 is offset from a second diameter section 97 by a shoulder 99. Aseries of spot welds 108 join the sleeve 96 to the metal shell 30.Thereafter a brazing material 110 in groove 42 is heated to atemperature such that it flows and forms a water and air tight sealadjacent the opened end 100.

A porous filter material 112 sold under the trade name of Zitex byNorton Chemplast, or an equivalent material which allows air to flowthrough while excluding water, is located in sleeve 96. A rubber gasket113 is located between openings 104, 104'. . . 104^(n) in the end 98 ofsleeve 96 and the filter 112. The rubber gasket 113 has a centralopening 115 and a series of axial openings 117, 117'. . . 117^(n) infilter material 112. Lead wires 106, 106'. . . 106^(n) extend throughthe openings 104, 104'. . . 104^(n), 117, 117; . . . 117^(n) and 114,114'. . . 114^(n) into the interior of the sleeve 96. The rubber gasket113 located between end 98 and the filter 112 has sufficient resiliencyto form a tight seal with the sleeve 96 and the insulating coating onleads 106, 106'. . . 106^(n) while at the same time its center opening115 allows air to be presented to filter 112 for communication tochamber 118. Because of the physical properties of filter 112 only dryreference air is presented to chamber 118.

A terminal member 120, as best shown in FIGS. 2, 3, 6 and 10, has afirst diameter section 122 separated from a second diameter section 124by a shoulder 126. First and second axial passages 128 and 130 extendfrom a first end 132 to a second end 134. A blind axial stepped bore 138extends from the second end 134 toward the first end 132. An axial slot136 in the terminal member 120 extends from the second end 134 to ashoulder 140. A first contact ring 142 attached to lead 106 is locatedon shoulder 140. A coil spring 146 which surrounds tubular heater 92 andforms an electrical flow path between contact ring 144 and cup 86. Aspring washer 148 surrounds the second diameter section 124 and acts oncontact ring 142 and flange 150 on carrier extension member 152. Carrierextension member 152 has a taper 154 on the end thereof which engagesboth the interior of carrier 66 and the opened end 76 of thimble ofsensor element 72. Spring washer 148 provides for an electrical flowpath whereby the external conductive surface 80 on sensor 72 isconnected to lead 106.

Terminal member 120 has first and second grooves 156 and 158 on theperiphery of the first diameter section 122 that extend to a firstradial slot 160 that extends along a diameter which is at substantiallya right angle to a plane through passages 128 and 130. A second slot 162is parallel to the first slot 160. Slots 160 and 162 while shownextending clear through the first diameter section 122 may under somecircumstances only extend to bore 138. Under normal operating conditionsgrooves 156 and 158, and slots 160 and 162, holes 128 and 130 act asflow paths for the communication of air from filter 112 into chamber118.

Terminal or contact member 164, see FIG. 7, has a flat surface 166 witha leg 168 extending therefrom. A central opening 170 is located on theflat surface 166 and has prongs or fingers 172, 172'. . . 172^(n) thatextend therefrom. Lead wires 106' is attached to leg 168 and flatsurface 166 is inserted into slots 160. When leg 168 engages the bottomof groove 156, opening 170 is located in the axial center of steppedbore 138. Similarly lead wire 106^(n) is attached to a second terminal164' and inserted into slot 162. When leg 168' engages the bottom ofgroove 158, opening 170' is located in the radial center of stepped bore138.

Heater 92, which is of the resistance type, has a first contact area 161and a second contact area 163 as shown in FIG. 10. When end 93 of thetubular member 90 of heater 92 engages the bottom 139 of bore 138, thefirst contact area 161 engages prongs 172, 172'. . . 172^(n) on terminal164' and the second contact area 163 engages prongs 172, 172'. . .172^(n) on terminal 164 to complete an electrical circuit fromcontroller 26. In addition to establishing an electrical circuit forheater 92, the prongs on terminal 164 and 164' resiliently engage thetubular member 90 to hold end 94 at desired position with respect to end74 of the thimble of sensor 72.

Each of the leads 106, 106'. . . 106^(n) is made up of several strandsof individual wires. As shown in FIG. 9, at first group of wires 174 arewound in a clockwise direction while a second group of wires 176 arewound in a counterclockwise direction. As can be seen, a spiral space isformed between the first and second wires 174 and 176. A plastic cover178 is placed on the outside of the wires 176 to prevent an electricalshort from affecting transmission between the controller 26 and sensor24. Further, this spiral space between the wires 174 and 176 provides anadditional flow path for the communication of air (reference gas) tochamber 118.

METHOD OF ASSEMBLY OF THE INVENTION

The exploded view of sensor 24 seen in FIG. 10 illustrates a preferredmethod of assembly of the individual component parts to create theheated and externally grounded electrolyte sensor for use in determiningthe oxygen content in the exhaust of an internal combustion engine.

In this assembly, a metal shell 30 is selected from a supply and a ringof brazing material 110 placed in a groove 42.

Thereafter a vented shield 50 is inserted in bore 32 in shell 50 untilflange 54 engages shoulder 46. A support 55 is inserted in bore 32 andpositioned against flange 54. A talc sealing ring 60 is placed in bore32 adjacent support member 57 and an insulating ring 56 placed on thetalc sealing ring 60.

A first carrier member 66 is then inserted in bore 32 and flange 68brought into engagement with the insulating ring 56. A tool is insertedinto bore 32 and acts on flange 68 and rib 78 to compress the talc ringand establish a seal between the thimble 72, metal shell 30 and carrier66. Under some circumstances a metal gasket may be required between rib78 and lip 70 to form a good electrical connection and gas seal betweensurface 30 and carrier 66.

The closed end 74 of sensor element 72 is inserted into carrier member66. External rib 78 engages the interior surface 69 of carrier member 66to form an electrical connection with the external surface coating 80.

Thereafter a carrier extension member 152 is located in bore 32 andforced into surface 69 on carrier member 66 until it engages rib 78 onthe sensor 72.

The assembly of the terminal end of the sensor element 24 starts bypulling leads 106, 106'. . . 106^(n) `through openings 104, 104'. . .104^(n) in closed end 98 of sleeve 96, openings 117, 117'. . . 117^(n)in rubber gasket 113 and openings 114, 114'. . . 114^(n) in filter 112located in sleeve 96 adjacent the closed end 98.

A first terminal 164 is attached to the end of lead wire 106" and asecond terminal 164' is attached to lead wire 106^(n).

Leads 106 and 106" are pulled through passages 128 and 130 in terminalmember 120 and contact rings 142 and 144 attached thereto. Lead 106" ispulled to seat contact ring 144 on shoulder 140 in bore 138. Similarlylead 106 is pulled to seat contact ring 142 onto shoulder 126.

Thereafter, the first terminal 164 is inserted into slot 160 and thesecond terminal 164' is inserted into slot 162.

End 93 of tubular heater 92 is inserted in bore 138 and is resilientlyengaged by prongs on terminals 164 and 164'. When end 93 contacts thebottom 139 of bore 138, surface areas 161 and 163 on tubular member 90will be in contact with prongs 172 of terminals 164 and 164' to form acomplete electrical current with leads 106' and 106^(n). Thereafter,wave or washer spring 148 is placed on cylindrical surface 124 andpositioned adjacent contact ring 142.

Coil spring 146 is placed over the tubular member 90 and end 145 broughtinto engagement with contact ring 144. A contact cup 86 is placed on thetubular surface 90 and brought into position adjacent end 147 of thecoil spring 146. Prongs 88 on cup 86 resiliently engage the tubularsurface so that the coil spring does not fall off if the terminalsection is placed in a vertical position with the heater member 92pointing toward the ground.

We now have essentially two individual assemblies which are to be joinedtogether to produce sensor 24.

Sleeve assembly 96 and shell assembly 30 are brought together as end 94on heater 92 is aligned with bore 81 of the thimble sensor 72. Contactcup 86 engages the interior surface of the opened end 76 of the sensor72 and sleeve 96 engages end 42 of metal shell 30 as end 94 is movedinto bore 81. A predetermined force, which moves the sleeve 96 and shell30 together, is maintained while spot welds 108 are made to join theparts together. As these parts are moved together, spring wsher 148 actson carrier extension 152 to hold tapered end 154 into engagement withsurface 69 of carrier 66 and link external conductive coating 80 on thethimble of sensor 72 with controller 26. At the same time spring 146moves contact cup 86 into engagement with the interior conductivesurface 82 to provide a link with ground terminal 27 in controller 26.

After the sleeve 96 and shell 30 are joined together by spot welds 108,flared flange 102 is subjected to heat which causes brazing material 110to flow and seal the joint therebetween. Visual inspection of thesurface 31 on metal shell 30 can determine if a seal has been achievedwith the brazing material 110.

Under some circumstances, the brazing can be replaced by crimping. Inthis situation, after sleeve 96 is spot welded to metal shell 30, thesensor 24 is transported to a station where a force is applied to a toolwhich acts on surface 96 to crimp surface 198 into groove 110 andprovide a water tight seal therebetween. This design may be moreeconomical since the flare 31 on sleeve 96 and the brazing material 110is not needed.

METHOD OF OPERATION OF THE INVENTION

When the internal combustion engine 16 is operating, exhaust gases areproduced and carried by pipe 22 to the environment. With sensor 24installed in pipe 22, the exhaust gases are communicated throughopenings 62, 62' in shield 50 to chamber 64.

Air from the environment is carried through filter 112 to chamber 118and to the interior coating 82 of the thimble of sensor 72.

Electrical current from controller 26 is carried on leads 106' and106^(n) to heater member 92. The resistance of heater member 92 is suchthat the temperature of the thimble is maintained above its minimumoperating temperature which for zirconium dioxide is above 350° C.

With changes in the ion flow between exterior conductive surface 80 andinterior conductive surface 82, an operational signal is carried on lead106 to controller 26. Since lead 106" is electrically grounded throughcontroller, the operational signal is an accurate measure of a change inion flow. The controller 26 evaluates the ion flow signal and generatesan operational signal which controls the air/fuel ratio supplied toengine 16 to maintain the exhaust gases within desired operationalstandards.

We claim:
 1. In an oxygen sensor having a solid electrolyte memberlocated in a metal shell and a terminal member located in a sleeve, saidsleeve being attached to the metal shell to define a reference chamberbetween said solid electrolyte member and said terminal member, saidterminal member retaining first and second contact leads which connectthe solid electrolyte member to a controller and third and fourthcontact leads that connect a heater associated with the solidelectrolyte member with said controller, said first, second, third andfourth contact leads extending through said sleeve, the improvement inthe sealing of said reference chamber from the surrounding environmentcomprising:an insulator ring and a sealing ring located between saidmetal shell and solid electrolyte member for sealing said referencechamber from the communication of exhaust gases when said sensor islocated in an exhaust pipe; a groove located in said metal shell; acrimped surface extending from said sleeve and located in said groove,said crimped surface establishing a seal to prevent communication of airand water into said reference chamber; a porous filter located adjacentsaid terminal member; and a rubber gasket located between said porousfilter and said sleeve, said first, second, third and fourth contactleads passing through said rubber gasket and said porous filter, saidfirst and second contact leads being connected to said solid electrolytemember and said third and fourth contact leads being connected to saidheater in said reference chamber, said rubber gasket axially biasingsaid porous filter into continual engagement with said terminal member,said porous filter having sufficient resiliency to engage said sleeveand said first, second, third and fourth contact leads to form a barrierto assure that only dry environmental air is presented to the referencechamber by preventing the entry of water into said reference chamber ispresented with substantially dry environmental air, said heatermaintaining said reference chamber above a present temperature such thatchanges in the oxygen content in the exhaust gases as compared to oxygenin the reference environmental air cause ions to flow in the electrolytemember, said changes in ion flow being presented to said controllerthrough said first and second contact leads to accurately indicate anoperational parameter of an engine as defined by exhaust gases.
 2. Inthe oxygen sensor as recited in claim 1 wherein said terminal memberincludes:first and second passages in which the first and second leadsare located, said environmental air freely flowing through the first andsecond passages into the reference chambers.
 3. In the oxygen sensor asrecited in claim 2 wherein said terminal member includes:first andsecond grooves located on the peripheral surface of the terminal memberthat extend to third and fourth passages in the terminal member, saidleads for the third and fourth leads being located in said first andsecond grooves and third and fourth passages to connect said heater tothe controller, said first and second grooves and third and fourthpassages providing additional flow paths for the environmental air intosaid reference chamber.
 4. In the oxygen sensor as recited in claim 3wherein said terminal member retains said first, second, third andfourth leads to establish independent first and second electricalcircuits, said first electrical circuit being connected to saidelectrolyte member while said second circuit is connected to the heater.5. In the oxygen sensor as recited in claim 1 wherein said sealingincludes:a brazing material located in said groove in said shell thatflows to establish a water tight seal.